This invention relates to an epoxy composition especially designed for use as a primer for sealing and filling small pores in concrete. Advantageously, the composition has the ability to cure at a low temperature (i.e., below about 32xc2x0 F./0xc2x0 C.), thereby extending the outdoor use of this sag-resistant epoxy primer through the winter months.
Epoxy resins have long been used for the priming and repair of concrete surfaces. However, the application of these materials are typically conducted at temperatures above freezing, i.e., above 32xc2x0 F. (0xc2x0 C.), and not below that temperature due to curing problems often encountered at temperatures below 32xc2x0 F.
previous attempts at preparing low temperature curing epoxy compositions have generally not progressed below about 40xc2x0 F. (about 4.5xc2x0 C.) as the low temperature cure cut-off point. For example, Rust-Oleum Corporation has advertised a low temperature activator (9103) for use with its System 9100 high performance epoxy resin. According to the company""s Internet literature, when the 9103 activator is used in the 9100 system, the coating can be applied and cured at temperatures as low as 40xc2x0 F. (about 4.5xc2x0 C.), which is ten degrees lower than the curing temperature lower limit for their standard activator. The 9100 epoxy coating is claimed to be suitable for use on abrasive blasted steel, concrete and masonry surfaces.
In American Paintand Coatings Journal, Vol. 80, No. 21 1996, p. 49, the Cardolite Corporation discloses the properties of three phenalkamine epoxy hardeners for epoxy coatings which can be used for marine and offshore coatings, industrial maintenance, pipe and tank linings, drinking water applications and concrete protection. One formulation (NC-541LV) is said to promote rapid cure at temperatures as low as 5xc2x0 C. (about 41xc2x0 F.).
In U.S. Pat. No. 4,221,890, a concrete repair material is disclosed which comprises a 100% solids epoxyamine composition comprising an epoxy resin, an aliphatic polyamine, a first accelerator comprising Bisphenol-A, a second polyamine composition and a second accelerator. The concrete repair material is claimed to have a cure temperature within the range of at least as low as 0xc2x0 F. (about xe2x88x9218xc2x0 C.) and at least as high as 140xc2x0 F. (about 60xc2x0 C.).
The need for suitable materials which will permit further coatings and afford a strong bond to concrete, and cure at temperatures below 32xc2x0 F. (0xc2x0 C.) continues. The present invention satisfies that need.
The present invention is directed to an epoxy primer that helps bond a fast-cure polyurea sprayable coating to a concrete surface. The key requirements of the epoxy primer of the present invention are:
1) Curable at low temperatures, preferably below 55xc2x0 F. (13xc2x0 C.), more preferably below 40xc2x0 F. (about 4.4xc2x0 C.), and most preferably below about 32xc2x0 F. (0xc2x0 C.);
2) High sag resistance, so as to fill xe2x80x9cbugxe2x80x9d holes in vertical concrete surfaces. Holes can be as much as 1 inch in width and depth, and sometimes even larger;
3) Good adhesion to concrete; and
4) Good adhesion to additional coating compositions, particularly polyurea coatings, sprayed on top of cured primer.
The present invention provides a composition which satisfies these criteria. In general, the composition is a two part system; Component A comprising the reactive epoxy resin mixture and Component B comprising the hardener or curing agent mixture.
The two parts are mixed before application, then the mixed primer is applied to the concrete surfaces to be primed and filled. The primer mixture can be mixed and applied manually (e.g., by trowel or sponge float) or by use of automatic metering, mixing and dispensing equipment. In supplying the primer composition as a two part system, each part is supplied in a separate container.
Component A comprises the following ingredients:
(a) from 75 to 115 parts by weight of a compound containing at least one glycidyl ether epoxide group;
(b) from 1 to 10 parts by weight of a Michael""s Addition agent, e.g., a polyfunctional acrylate monomer;
(c) from 0 to 1 part by weight of color concentrate (e.g., grey);
(d) from 0 to 10 parts by weight of filler and/or thickener materials; and
(e) from 1 to 10 parts by weight of a diluent to maintain a low viscosity at low application temperatures.
Depending on the epoxy used, the diluent used, and the amount and types of thickeners and/or fillers used, viscosity of Component A may be in the range from 1000 cps to 300,000 cps, with a preferred range being 10,000 cps to 100,000 cps, and a most preferred range being 25,000 cps to 75,000 cps. One currently preferred embodiment has a viscosity of about 53,000 cps.
The epoxy resin used herein must resist crystallization and thickening at low temperatures, thereby allowing easy application of the primer. The reactive epoxy mixture of the present invention advantageously comprises a bisphenol-epichlorohydrin epoxy resin having an epoxy equivalent weight ranging from 150 to 250. The epoxy equivalent weight is defined as the weight in grams of the resin containing one gram equivalent of epoxide. Suitable epoxy resins of this type are commercially available from the Shell Chemical Company, Resins and Versatics Sales Office, Houston, Tex. under the trademark Epon(copyright). The currently most preferred epoxy resins are Epon 862 and Epon 828.
In addition to the epoxy resin, Component A of the present invention further comprises at least one Michael""s Addition agent. This agent is added to enhance the low temperature reaction with the curing agent. Suitable materials of this type include polyfunctional acrylate monomers which participate in a very rapid Michael""s Addition reaction with the primary amine functional groups present in the curing agent. The addition of such a reactive agent assists the curing process at low temperatures, maintaining satisfactory cure rates even at temperatures of about 25xc2x0 F. (about xe2x88x924xc2x0 C.) or less. One commercially available polyfunctional acrylate monomer of this type is Photomer 4399 from the Henkel Corporation.
As described above, Component A further comprises coloring agents, filler and/or thickener materials, and diluents. Examples of suitable filler and/or thickener materials include fumed silicas, and similar inorganic solids. Diluents include alcohols and the like. Currently preferred materials include Cab-O-Sil TS-720 and benzyl alcohol. Color concentrates for a variety of colors (e.g., grey) are widely available.
Component B comprises the following ingredients:
(aa) from 65 to 105 parts by weight of an amine-based hardener, for example, a Mannich Base curing agent;
(bb) from 12 to 18 parts by weight of an amine-based accelerator;
(cc) from 0 to 1 part by weight of a color concentrate (e.g., grey);
(dd) from 0 to 6 parts by weight of one or more thickener materials; and
(ee) from 4 to 6 parts by weight of a diluent to maintain a low viscosity at low application temperatures.
Depending on the materials used, the viscosity of Component B may be in the range from 100 cps to 100,000 cps, with a preferred range being 1000 cps to 50,000 cps, and a most preferred range being 10,000 cps to 50,000 cps. One currently preferred embodiment has a viscosity of about 14,400 cps.
The hardener or curing agent mixture (Component B) advantageously comprises components that react suitably with the reactive ingredients in the Component A mixture, to afford a suitable primer composition that will cure at temperatures below about 32xc2x0 F. (0xc2x0 C.). One preferred class of curing agents makes use of xe2x80x9cMannich Basexe2x80x9d chemistry, which reacts rapidly with the Epon epoxy resins, and even more rapidly with the Photomer 4399, present in the resin mixture.
Mannich Bases, as preferred amine-based components of curing agent composition, are of value in reducing the cure time and they improve strength of the primer bonding. The amines for making Mannich Bases may be primary or secondary; they may be diamines or other polyamines. The Ancamine family of curing agents, commercially available from Air Products and Chemicals, Inc., Allentown, Pa., are within this class. In the present invention the preferred amine is triethylenetetramine (TETA). An especially preferred Mannich Base curing agent based upon TETA is Ancamine 1637.
Ancamine K54 (Air Products and Chemicals) and Capcure EH-30 (Henkel Corporation) are examples of a preferred amine-based accelerator for use herein. These products are the same material, namely 2,4,6-tri(dimethyl-aminomethyl)-phenol, a tertiary amine which catalyzes the epoxy curing reaction to high rates.
Diluents may be reactive or nonreactive. Alcohols have been found to be suitable for use as the nonreactive diluent in both Component A and Component B. Benzyl alcohol is an example of a preferred non-reactive diluent which keeps the viscosity low in cold environment. Reactive diluents have one or more functional groups that react with one or more of the other components in the mixture. Examples of suitable reactive diluents include epoxy-functional glycidyl ethers, for example, butyl-glycidyl ether, 2-ethylhexyl-glycidyl ether and cresyl-glycidyl ether, to name a few.
Fillers which may be used in either of the two parts include talc, kaolin, silica, aluminum and other metal powders, metal oxides, calcium carbonate and the like.
Thickening agents (i.e., thixotropic agents) include silicas and similar materials. Preferred thickening agents are the fumed silicas, such as those sold under the tradenames Cabosil (Cabot Corp.) or Aerosil (Degussa). Cab-O-Sil TS 720 has been found to be an especially preferred embodiment of the fumed silicas useful herein. Combinations of one or more thickeners and/or fillers may also be employed herein.
An especially preferred formulation meeting all of the above requirements can be prepared by mixing the following two component (resin and hardener) compositions:
Component A (Resin):
Component B (Hardener):
An especially preferred primer composition was prepared using 74.8 parts by weight of Component A and 25.2 parts by weight of Component B. This primer composition (100 grams) had a gel time at 75xc2x0 F. (24xc2x0 C.) of about six (6) minutes. The thin film set time (TFST) for this primer composition, at a temperature range of 25xc2x0 to 32xc2x0 F. (xe2x88x924xc2x0 to 0xc2x0 C.), was from about eight (8) to sixteen (16) hours. The TFST at a temperature range of 40xc2x0 to 50xc2x0 F. (4.4xc2x0 to 10xc2x0 C.) was from about two (2) to six (6) hours.
The measured adhesion strength of this primer composition to polyurea was greater than 200 psi, preferably at least 300 psi, and most preferably at least 400 psi, as measured on an Elcometer using test method ASTM D 4541.